Originally Posted By: unimogbert
Originally Posted By: dougwalkabout
but I suspect the trick is to take some time and charge the weak battery at low revs. Then start the weak vehicle, keeping low revs on the charging vehicle.


Reason you don't want to connect post to post is that there will be a spark generated on making the final (4th) connection. You don't want that spark to be close to the top of the battery where hydrogen gas from charging is generated. The spark could propagate into the space above the cells and blow up the battery. (or so I'm told) Having a battery blow up in your face would be a very bad thing.


I agree that a hydrogen/battery explosion is the primary concern. I was always told that grounding on the frame ensured the primary current path was through the starter and only a secondary current would pass through the battery (thus generating less hydrogen).

Grounding to frame on the dead vehicle is the safe and proper way to do it. Unfortunately, many vehicles don't provide a good frame grounding point that a clamp can hold on to.

(A clarification: by "low revs" I didn't mean idling. You have to rev up a little to charge the dead battery; the bigger the battery, the longer it will take to put a partial charge on it.)


Edited by dougwalkabout (12/09/12 05:48 PM)